1,721,204 research outputs found
Experimental Study of Longitudinal Stage Separation of Two-Body Configuration in Shock Tunnel
No full textThis study is the first to report the tests of a parallel-staged TSTO model with dynamic longitudinal stage separation (LSS) at different AoA values in the JF-12 hypersonic flight duplicated shock tunnel. The high-speed PED is developed for the dynamic test technique in shock tunnel. Static tests show the good aerodynamic performance of the TSTO model. Dynamic tests show that the small stage gap of LSS leads to weak type I and VI SSI, with short-time weak shock reflection and weak oblique SBLI in the flowfield at high AoA values. Furthermore, no shock reflection or weak oblique SBLI is observed in LSS at small AoA values, so the aerodynamic interference of LSS is weak. In addition, although the orbiter exhibits a smooth separation maneuver in both LSS tests, it tends to fly in a nose-up attitude at AoA = 8.3 deg and a nose-down flight attitude at AoA = 4.5 deg. Hence, the most appropriate AoA condition for the LSS of the TSTO model may be expected in the middle of 4.5 and 8.3 deg. No stage recontact is observed during LSS, and the safety and feasibility of LSS for the parallel-staged TSTO model are demonstrated experimentally, which is important for the success of the future TSTO system.</p
Numerical Investigation of Aerodynamic Separation Schemes for Two-Stage-to-Orbit-like Two-body System
No full textTwo-stage-to-orbit (TSTO) hypersonic vehicle is considered one of the most promising next-generation reusable launch vehicle (RLV) systems for its efficiency and reliability, but the safe separation of two-body system determines the success of TSTO missions. Hypersonic flows around a TSTO-like two-body system are studied by CFD (computational fluid dynamics) dynamic simulations at Mach 7. The TSTO model, which consists of two three-dimensional (3-D) wedges as orbiter and booster, is used to investigate the interstage aerodynamic interferences and separation characteristics with different stage separation schemes. This paper analyzes in detail the transverse stage separation (TSS) scheme, where the orbiter moves along the direction normal to the upper surface of the booster. Besides, the longitudinal stage separation (LSS) scheme, in which the orbiter moves rapidly along the flight direction of the booster, is proposed. The numerical results of dynamic simulation show that the complex interstage aerodynamic interference is accompanied by the combined action, including the disturbance of wave/boundary-layer interaction, shock/wake-flow interaction, and a horseshoe vortex (or a “˄” vortex). Moreover, the flow characteristics and the physical mechanism of TSTO separation are clarified by analyzing the changes of flow structure and the topologies of 3-D separation flow. The intensity of the aerodynamic interference increases with increasing angle of incidence (AoI), but decreases with the increase of clearance during TSS. The ideal values of AoI for TSTO TSS are 6° and 8°. For LSS, the orbiter can safely separate from the booster at angle of attack (AoA) = 5° and 10° cases while the collision occurs at AoA = 0° case. The proper AoA value of the safe LSS is 5°. Since the interference load on the stages in LSS is smaller than that in TSS, the LSS is ideal for stage separation of TSTO.</p
Numerical Investigation on Longitudinal Stage Separation of Spiked Two-Stage-to-Orbit Vehicle
No full textA longitudinal stage separation (LSS) scheme for a parallel-arrangement two-stage-to-orbit (TSTO) vehicle is proposed and analyzed in detail, in which the orbiter moves along the upper surface of the booster. A TSTO concept comprising a waverider and a spaceplane was designed to numerically investigate the dynamic characteristics of the LSS at Mach 7. The influence of spike models assembled at the nose of the orbiter on the LSS at different angles of attack (AoA) (i.e., spike with half cone, spike with half cone-disk, and hemispheric spike) was explored. Moreover, the aerodynamic interference and characteristics were analyzed and compared for different spiked configurations. The aerodynamic interference during LSS is simple and weak, which is only associated with type VI shock/shock interaction, with rapid increases in the axial force when the shock waves of both stages converge. Furthermore, the model with a half cone spike has the best performance in drag reduction by 7%, whereas the model with a half cone-disk spike has the worst performance that increases axial force. The TSTO model with a half cone spike at AoA=0 and 5 deg is advantageous in LSS because of the high drag reduction and weak aerodynamic interference.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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